1. Field of the Invention
The invention pertains to stackable and portable data carriers including a card-shaped carrier element, on which there are disposed at least one electrically programmable, non-volatile semiconductor memory and at least one external connection of the data carrier that is electrically connected to the memory. The external connection has contact faces disposed on the surfaces of the data carrier in such a way that when data carriers of the same kind are resting on one another, they electrically contact the respective neighboring data carriers and a bus system at the same time.
Data carriers with standardized dimensions have been known in the art generally as chip cards. Conventional chip cards contain semiconductor elements with relatively small storage capacity and a logic circuit in the foreground. With the increasing availability of semiconductor memories that can be inexpensively produced and that have a storage capacity at least in the megabyte range, comes the desire to rapidly and easily access a large number of data carriers of the same kind with the greatest possible storage capacity. These data carriers are intended, for example, for digitized music signals, image signals received by an electronic camera, texts (such as entire dictionaries), electronic maps, software for data processing systems, etc. The semiconductors can be writable and erasable memories or read-only memories (ROM). The data are preferably stored in a compressed format with regard to their redundancy.
2. Description of the Related Art
Commonly owned, copending application Ser. No. 08/828,697, filed Mar. 31, 1997 (publ. WO 96/10804), which is here incorporated by reference, describes a stackable data carrier of the above-mentioned kind. There, the contact faces should preferably be disposed running flush around one of the edge faces of the carrier element. As a result, a number of these cards can be easily stacked one on top of the other so that a large number of data carriers of the same kind can be simultaneously connected to a processing device without an expensive additional device. Connection faces that run flush around an edge achieve a direct reciprocal contacting of the cards stacked on top of each other without a contact rail. Mention is also made of a loosely manageable connecting socket that secures the stacked data carrier cards in a mechanically fixed composite unit.
The corresponding connections, which are directly or indirectly connected to one another and belong to a number of cards disposed one on top of the other, function logically as a data bus so that all of the data carriers of the stack are simultaneously connected on-line the moment even one of the stacked data carriers is connected to the device.
The copending application further proposes, in connection with the possibility of combining a number of mutually stacked data carrier cards in a connecting piece or in a housing, positioning means which force the chip cards as precisely on top of one another as possible and, as a result, assure an exact overlapping of their connections. These positioning means include at least one projection on a main face of the carrier element and a corresponding recess on the opposite main face, which can receive the projection of another data carrier. The knob-like projections disclosed there, however, particularly due to insufficient elasticity, are not suited to assure a durable fixing of the stacked data carriers even with the exertion of external force. Furthermore, even with an exact overlap of the connections, no assurance of sufficient contact force or a tolerance compensation in the stacking direction between the different connection contact points is made.